Evolutionary history constrains heat tolerance of native and exotic tropical Zingiberales

Tropical wet forest plants experience relatively stable temperatures throughout the year. However, tropical forests represent a mosaic of habitats characterized by different temperatures. Heat tolerances are expected to be adapted to temperatures specific to their habitats. Although heat tolerance of species sharing similar environments is expected to be similar, it is also possible that heat tolerance is constrained by evolutionary history because closely related species usually display similar physiologies. When exotic species are introduced to novel communities, colonization may be facilitated by their previous adaptation to high temperatures and other physiological, genetic and demographic traits, which may grant them some competitive advantage. Increasing temperatures may represent a strong environmental filter affecting community assembly, and higher heat tolerances could facilitate the persistence of exotic species in novel environments. Using a community of 32 native and 7 exotic Zingiberales species from different tropical habitats in Costa Rica, Central America, we aim to answer the following questions: (a) does evolutionary history constrain heat tolerance? (b) do plants in the same habitat display similar heat tolerances? (c) do the heat tolerances of exotic species differ from those of native species? We measured temperature-dependent changes in photosynthetic fluorescence to determine the temperature at which the first sign of damage to photosystem II is observed (T-15), and the temperature at which the fluorescence of photosystem II is reduced by 50% (T-50). Using a community phylogeny, we tested for phylogenetic signal in T-15 and T-50. In addition, we tested for differences in heat tolerance among Zingiberales from old growth, secondary forests and open areas, as well as between native and exotic species. Our results support (a) a significant phylogenetic signal (Pagel's lambda) for both T-15 and T-50, (b) communities from open areas displayed similar photosynthetic heat tolerance compared to species from old growth and secondary forests, and (c) exotic Zingiberales are marginally tolerant to high temperatures than native species, but only for T-15. Our results suggest that evolutionary history constraints heat responses of native and exotic Zingiberales in a warming world. Read the free Plain Language Summary for this article on the Journal blog.